Mike Mulholland | MLive.comBill Bentley has flashed potential in practice and on Sundays, but Detroit Lions general manager Martin Mayhew expects the third-year cornerback to start putting it all together this season.

ALLEN PARK -- The Detroit Lions selected three cornerbacks in the 2012 draft -- taking Louisiana-Lafayette's Bill Bentley in the third round, local standout Chris Greenwood in the fifth and New Mexico State speedster Jonte Green in the sixth.

All three have seen the field for the Lions in the past two seasons. And while the trio has flashed the potential that landed them in Detroit, their future with the organization hinges on what they do this year, according to general manager Martin Mayhew.

"Some guys walk in from day one and they've got it," Mayhew said on Monday. "They just step on the field and they've got it. Some guys take a year, some guys take two years. It doesn't take more than three years.

"If you don't have it in three years, you don't have it," he continued. "So this is a big year for those guys. It's a big year to see where they are. I like what I've seen thus far."

Bentley is the most likely to still be on the roster at the start of the season. The team's primary nickelback in 2013, he appeared in 13 games, making 29 tackles and breaking up five passes.

After a rough start to the season, which included a bad pass interference call in the closing minutes of a road loss to Arizona, Bentley showed more consistency down the stretch. Disappointingly, after displaying decent balls skills in college, he's still looking for his first professional interception.

Green was a bit of a forgotten man until late in the 2013 season, one year after injuries forced him into a significant role as a rookie. He appeared in 15 games in 2012, including five starts. He was arguably the team's most impactful first-year player that season, making 29 stops, breaking up four passes and snagging an interception.

Greenwood missed his entire rookie campaign with an abdominal injury and was part of the team's final wave of cuts before the regular season in 2013. He was signed to the team's practice squad, but was poached by Dallas in the middle of the year. After a short stint with the Cowboys, Greenwood returned to Detroit, appearing in his first three games at the end of the season.

Mayhew wants to see the trio display the relentless competitiveness he expects from his defensive backs.

"As far as corners, I think I said before, the most important thing to me is competitiveness," Mayhew said. "You've got to have that guy that doesn't want anybody catching any balls on him ever in practice, in walk-through, whatever. We're looking for a guy that has that kind of mentality. A lot of them have different physical attributes, but the mentality is the most important thing at corner I think."

Green and Greenwood will enter camp competing for backup roles behind last year's second-round pick Darius Slay and veterans Chris Houston and Rashean Mathis. The Lions could also draft a cornerback later this week, as early as the first round.